Unknown Health Concern

Question
My pet rat who's about a year old was completely fine the other day but when I went to check on him today he was missing both his top teeth and was rolled over on his side with the other side in the air. He seems to be in a lot of pain and I can't touch him without him squealing. He lives with two other male rats but they never fight. There was no blood on him or anywhere in the cage.I have owned rats before and have never seen anything like this before. Do you have any idea what this could be?

Answer
Sounds like for starters he may have malocclusion which would be the reason for his teeth missing. Malocclusion causes teeth to be misaligned and they can break off at the gumline. Malocclusion can occur as a birth defect and if the teeth are not trimmed as they get older, the teeth can rub right into the roof of the mouth etc... but sometimes they can also break as well. There is a misconception that if you supply your rat with chewing toys this will keep their teeth from growing too much, but the truth is, if the rat does not have a misaligned jaw, normal chewing will grind up the food. Also, when a rat bruxes, this also helps.  You will need a vet for him to get him checked over and to rule out anything else that could be causing him to not be able to use his mouth and teeth properly.
Sometimes a pituitary tumor can cause the rat to be unable to chew properly due to the inability to control the muscles of the face and mouth.  Steroids can help for a little while. You can help him eat buy giving him some baby food and making sure he drinks water even by a dropper.

Can he move about now?  Do you have a good vet?